DEARBORN - A semitruck jackknifed on the southbound Southfield Freeway at Oakwood Boulevard during a heavy snowstorm at about 12:30 p.m. Saturday.?About a dozen other vehicles crashed as a result.? Emergency crews from Dearborn, Dearborn Heights, Allen Park, Melvindale and Wyandotte responded, as did private ambulances. Crews from as far away as Brownstown Township and Trenton also were called.?